1. Field of the Invention
This invention relates to an improved silica-alumina composite. More particularly, the invention relates to an extruded silica-alumina base catalyst exhibiting surprisingly little deactivation in the dentrification of petroleum feedstocks.
2. Prior Art
The prior art teaches a plethora of methods useful in the manufacture of silica-alumina composites. Such composites may be prepared for use as catalysts per se or as catalyst supports. Silica-alumina composites have been commercially embraced for a variety of process applications, such as cracking, desulfurization, demetallation, and dentrification of petroleum feedstocks.
The variety of manufacturing techniques presented in the art, which have been recognized as patentably distinct modifications, attest to the fact that the final catalyst properties are highly dependent upon the precise method of manufacture. Such variety, with seemingly subtle differences, is also an indicia of the unpredictability of catalyst manufacturing procedures in general. The change of a single step to another apparently equivalent step may result in a more desirable pore structure, increased activity, lower deactivation rates, higher crush strengths or a totally worthless product. Despite major advances in the art, as exhibited by great numbers of new emerging catalysts, the effect upon the final catalyst of changing a single step cannot be predicted with certainty, and thus most catalyst research continues by laborious trial and error.
Numerous prior art references teach that the combinations of metals, their oxides and sulfides, from Group VI-B and Group VIII of the Periodic Chart are useful for desulfurization and dentrification. Such metals may be impregnated upon preformed bases or supports, such as alumina and silica-alumina supports, by immersing the base in a solution of the metals. Alternatively, the metals may be precipitated or cogelled with the base. Heretofore, the deposition of metals by precipitation or cogellation was considered to be superior to impregnation of the metals on the base, since the latter method tended to produce non-uniform deposits of active metals. The increased costs of production inherent in cogellation or precipitation over impregnation were simply borne in order to obtain a more uniform product.
A unique method of preparing mulled catalyst extrudates based on silica-alumina cogels has been discovered which results in preparation of a hydrodenitrification catalyst having substantial advantages over the prior art impregnated catalysts and equivalent to the prior art cogelled or precipitated catalysts. In particular, the catalyst exhibits a deactivation rate of approximately one-fifth that of similar commercial catalysts.